Cracking hydrocarbon oils



Jan. 3, 1939. E, NELSQN 2,142,675

Y CRAGKING HYDROC-ARBON OILS FiledFeb.' 8, 1956 (orzafeus'ew ya {17"7762 Ce Coole?" Patented Jan. 3, 1939 UNiTED n STATES PATENT OFFICE 2,142,675 c CRACKING HYDROC'ARBON OILS Edwin F.-Nelson, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware `Application February 8, 1936, Serial No. 462,923

11 Claims.

This is a continuation-in-part of my co-pending application Serial No. 638,099, led October The invention particularly refers to an improved process for the selective pyrolytic conversion of relatively low-boiling and high-boiling ,hydrocarbon oils to produce therefrom high yields of good quality motor fuel with the simultaneous production of two heavy residual products of independently controlled characteristics.

It has become common practice in modern cracking operations to recover end-point motor fuel as the nal light distillate product of the process, returning the total higher boiling fractions of the vaporous conversion products to fur- Vther cracking, together with the'charging stock.

, This type of operation not only gives increased sion products which formerly constituted that portion of the pressure distillate boiling above the range of the desired final motor fuel pro-duct.

However, due to the relatively refractory nature of this material and the fact that it cannot be recracked under the most advantageous conditions when commingled with higher boiling oils, i y such as heavy charging stock and'higher boiling fractions cf the intermediate liquid conversion products, a considerable yfurther improvement has been obtained in practice by separating such relatively refractory material from the higher boiling oils and subjecting the same to independently controlled cracking conditions in a separate heating coil. This practice, which is now used extensively, permits the use of more severe cracking conditions in said separate heating coil than that to which the higher boiling oils are subjected in the heating coil of the system to which they are supplied, resulting in a higher degree of conversion of the relatively light oils per pass through the heating coil and a higher yield of motor fuel of even better antiknock value, eliminating, at the same time, theV decreased capacity of the process, previously encountered, due to continuous recycling, Without extensive cracking, of relatively large quantities of the light intermediate products.

The previous practice in selective cracking operationsof this type has been to commingle the These improvements are,lof course,

, lighter oils.

residual liquid conversion products from both cracking steps and subjectthe commingled materials to appreciable further vaporizationat substantially reduced pressure relative to that at which they are formed, the resulting product l normally being ,either a relatively heavy liquid 'residue or relatively dry petroleum coke. I have found, however, that when a selective cracking system is operated in this manner the com- .mingled kresidual liquid product is often of inferior `quality as comparedto that resulting from cracking of either the relatively low-boiling or the relatively high-boiling oil, in other words,

residual liquid products of quite dissimilar char- Yasphaltic'residue upon cracking, since the operating conditions might often be controlled, in

Vsuch cases, to producemarketable asphalt or road oil as the residual product if it were not contaminated with the substantially non-as-` phaltic residue resulting from cracking of the On the other hand, a good quality marketable fuel oil residue might often be produced by cracking of the relatively light oilsif it were not contaminated with the relatively heavy asphaltic residue resulting from cracking of heavy charging stock and/or high-boiling intermediate liquid conversion products of the process.

The present process retains all of the advan-` tages resulting from the selective conversion of relatively low-boiling and high-boiling oils and in addition provides for the recovery of a separate residual liquid product from the light oil and heavy oil `cracking step, the total vaporous conversion products from both steps preferably being subjected to fractionation in commingled state whereby the components of both boiling above the range of the desired final motor fuel product of the process are separated into selected relatively low-boiling and high-boiling fractions, the latter being returned to the heavy oil cracking step and the former to the light oil cracking step.

While the invention is particularly advantageous as applied to cracking operations emy, ploying charging vstock which may be mildly cracked to yield an asphaltic residual liquid or semi-liquid product, it is not intended to limit the invention to the processing of any particular type of charging stock nor to the production of any specific residual liquid product in either the light oil or heavy oil cracking stage of the system. The features of the invention are applicable to any economic condition which may make it desirable to produce separate residual products from light oil and heavy oil cracking operations` In one embodiment, the invention comprises subjecting charging stock, comprising a hydrocarbon oil of relatively wide boiling range containing an appreciable quantity of relatively highboiling fractions which may be mildly cracked to produce substantial yields of asphaltic residue and lower boiling oils, to fractional distillation, together with vaporous conversion products of the process whereby the components of the charging stock and vaporous conversion products boiling above the range of motor fuel are separated into relatively high-boiling fractions containing said asphalt-producing materials and lower boillng fractions which will not yield any substantial quantity of good quality asphaltic residuebycracking, subjecting the relativelyhigh-boiling fractions to relatively mild conversion conditions of cracking temperature and 'superatmospheric pressure regulated to effect the production of marketable heavy asphaltic residue and lower-boiling products, subjecting the liquid products resulting from said cracking to appreciable vaporization in a zone of substantially reduced pressure relative to that at'which they are produced to separate said marketable asphaltic residue from their lower boiling components, recovering said asphaltic residue, subjecting the vaporous products of the cracking and vaporizing operations to said fractionation, separately subjecting said low-boiling fractions recovered from the fractionating step to independently controlled conversion conditions of superatmospheric pressure and higher cracking temperature regulated to effect the production therefrom of high yields of good antiknock motor fuel, separating the resultant Vaporous and nonvaporous conversion products out of contact with the asphaltic residue produced in the first mentioned cracking operation, subjecting the vaporous products of said separate cracking operation to said fractionation, subjecting fractionated vapors, comprising materials within the boiling range of the desired motor fuel product and gases, to condensation and recovering -and separating the resulting distillate and gas.

As a means of assisting control of the first mentioned cracking operation to prevent excessive conversion and consequent destruction or deterioration of the asphaltic product, the invention provides for cooling either the total or the liquid conversion products in this stage of the system. This may be accomplished in any suitable manner, several of which are now well known, but in the preferred embodiment of the invention I use, as cooling material, a relatively low-boiling hydrocarbon oil which, after being commingled with the relatively hot conversion products and serving to cool the same, will be revaporized and hence will not contaminate the final residual product. This cooling material may comprise, for example, a regulated quantity of said low-boiling fractions recovered from the fractionating step and is preferably cooled, prior to being commingled with the conversion products of the heavy oil cracking operation, in order to reduce the volume of cooling oil required to effect the desired temperature reduction.

Preferably, the relatively low-boiling fractions subjected to conversion in the second cracking stage of the system, for the production, primarily, of high yields of good quality motor fuel, include substantially all of the intermediate liquid con- Version products boiling lower than approximately 600 F., and also preferably include any components of the charging stock of similar boiling characteristics. This is particularly desirable when the process is operated for the production of asphaltic residue as the residual product of the heavy oil cracking step since I have found that, inY most cases, when the heavy oil stream contains any substantial quantity of materials, (particularly cracked products), boiling below approximately 600 F. the resulting residual liquid product will normally contain an excessive quantity of nonasphaltic materials. On the other hand, when the cracking conditions to which the heavy oil stream is subjected are maintained sufficiently mild to preclude substantial cracking of any relatively low-boiling oils included therein recycling of the latter to the heavy oil cracking coil serves no useful purpose and simply increases the heat load and decreases the capacity of this stage'of the system. This particular phase of the operation will, of course, vary somewhat with different charging stocks and it may be desirable, in some cases, to include, in the light oil stream, substantially all of the material boiling, for example, up to 650 F. The initial boiling point of this fraction will, of course, vary depending upon the desired end-boiling point of the final motor fuel product of the process but in most cases will range, for example, from 360 to I10" F.

The accompanying diagrammatic drawing illustrates one specific form of apparatus embodying the features of the invention above mentioned and in which the desired results may be accomplished. Some of the many possible alternatives, not previously mentioned, which may be employed without departing from the scope of the invention, are also illustrated in the drawing and included in the following description thereof.

Referring to the drawing, raw oil charging stock for the process, which may comprise any desired type of hydrocarbon oil, is supplied through line l and valve 2 to pump 3 by means of which it may be fed through line 4, valve 5 and line 6 to heating coil 1. However, when desired, and particularly in case the raw oil contains any substantial quantity of relatively low-boiling materials which will yield, upon cracking, products detrimental to the production of the desired residual product in the heavy oil cracking stage of the system, it may be supplied from pump 3 through line 8 and valve 9 into fractionator I0 wherein it is subjected to vaporization and fractionation together with the vaporous conversion products, whereby high-boiling components of the commingled materials, suitable for relatively mild cracking to produce the desired residual liquid product, are separated from their lower boiling components.

The desired relatively high-boiling oils, comprising high-boiling fractions of the reflux condensate formed in fractionator I0, either alone or together with the total or high-boiling fractions of the charging stock, are directed through line 24 and valve 25 to pump 26 by means of which this material is fed through line 6 and valve 21 to heating coil '1.

A suitable furnace Il supplies the required heat to the relatively heavy oil passing through heating coil 'l to subject the same to the desired conversion conditions of relatively mildcracking temperature and substantial superatmospheric pressure. The heatedv products are discharged from heating coil 1 through line I2 and may be directedeither through valve I3 in this line to reaction chamber I4 or through line I2', valve I3 and line I5 into vaporizing and separating chamber I1.

Chamber I4, when this zone is employed, is preferably operated at a substantial superatmospheric pressure and, although not indicated in the drawing, this zone is preferably insulated to prevent the excessive loss of heat therefrom by radiation. Chamber I4 is preferably employed when appreciable continued cracking of the heated product from coil 'I is desired prior to separation of the residual liquid and preferably it is operated in the manner, now well known in the art, whereby the vaporous products are subjected to more prolonged conversion time in this zone than the liquid products. Both. vaporous and liquid conversion products may, when desired, be removed in commingled state from the lower portion of chamber I4 and directed therefrom through line I5 and Valve I6 to vaporizing and separating chamber I1. The invention also contemplates Aseparate removal of a regulated portion or all the vaporous products from chamber i4, provision being made in the drawing for withdrawing the same from the upper portion of this zone by directing the same through line i8 and valve I9 to fractionation in fractionator l0. When desired, a portion or all of the vaporous products'separately removed from chamber I4' may be introduced into chamber I1 at any desired point in this Zone, by well known means not illustrated.

Chamber I1 is preferably operated at a substantially reduced pressure relative to that employed at the outlet from heating coil 1 and relative to that employed in chamber I4, when the latter zone is utilized. By virtue of the reduced pressure employed in chamber I1 appreciable further Vaporization of the liquid conversion products supplied thereto from chamber I4 or heating coil 1 is accomplished therein and the pressure reduction also serves to assist cooling and retard or arrest conversion of the heated products supplied to chamber I1. The liquid residue remaining unvaporized in chamber I1 is removed from the lower portion of this rone and may be directed through line 20 and `valve 2| to cooling and storage or elsewhere, as desired. Vaporous products are removed from the upper portion of chamber I1 and directed through lin-e 22, valve 23 and line I8 to fractionation in fractionator I0, preferably in commingled state with the other vaporous cracked products of the process.

The characteristics of the residual product recovered from chamber I1 will vary with the nature of the charging stock or, more particularly, the nature of the high-boiling oils supplied to heating coil 'I and the cracking conditions to which they are subjected. With certain types of charging'stock and suitable cracking conditions this product may comprise marketable asphalt or road oil but, although this method of operation comprises one of the preferred embodiments of the invention, it is not limited to the production of asphaltic residue in chamber I1 and the chief distinguishing characteristic of this product is not so much its specific nature, since this may vary vwith the cracking stocksupplied to heating coil 1 and the operating conditions employed,. but is rather its lack of contamination with residual products resulting from the cracking of relatively low-boiling oil and particularly those boiling below approximately 600 F.

When the residual liquid produced in chamber I1 is of an asphaltic nature it is within the scope of the invention after reducing the same to a relatively heavy viscous residue in chamber I1 to remove the same to a separate asphalt-producing zone, not indicated in the drawing, wherein it may be blown with air or steam to produce a marketable asphalt of the desired characteristics or it may be so treated in chamber I1, although a separate zone is preferably employed when treatment with air or steam is required to produce the desired product.

The .vaporous cracked products supplied to fractionator I0 are subjected to fractionation in this zone, either alone or together with a portion or all of the hydrocarbon oil charging stock for the process, whereby their components boiling above the range of the desired nal light distillate product of the process (preferably comprising essentially motor fuel) are condensed and separated into relatively low-boiling vand highboiling fractions. The high-boiling fractions,

- preferably containing no substantial quantity of materials boiling below approximately 600 F., are returned, in the manner previously described, to cracking in heating coil 1. The relatively lowboiling fractions, comprising materials suitable for more severe cracking to produce high yields of good quality motor fuel, are separately removed from one or a plurality of suitable intermediate points in the fractionator; provision being made in the case here illustrated for directing the same through line 38 and valve 39 to pump 40 by means of which they are fed through line 4I valve 42 and line 43 to heating coil 44.

It is also within the scope of the invention, when desired, to employ a secondary charging stock preferably comprising a relatively low-boiling oil `suitable for cracking under the same conditions to which the relatively low-boiling intermediate products from fractionator I0 are subjected in heating coil 44 to produce high yields of good quality motor fuel and a residual product similar to that resulting from such cracking of said relatively low-boiling intermediate products. This secondary charging stock, when employed, is supplied through line 45 and valve 46 to pump 41 by means of which it is fed through line 43 and Valve 48 to heating coil 44.

Suicient heat is supplied to the oil passing throughheating coil 44, by means of a suitable furnace 49, to subject the same to the desired temperature, preferably at a substantial superatmospheric pressure. The heated products are discharged from heating coil 44 through line 50 and valve 5I into reaction chamber 52.

Chamber 52 is also preferably maintained at a substantial superatmospheric pressure which may be substantially the same or somewhat lower than that employed atl the outlet from heating coil 44. Chamber 52 is also preferably insulated, although this is not indicated inthe drawing, to conserve heat so that the heated products supplied to this zone from heating coil 44 and, more particularly, their vaporous components are subjected'to appreciable further conversion therein. Both vaporous and liquid conversion products are withdrawn, in the case here illustrated, from the lower portion of chamber 52 and directed through line 53 and valve 54 to vaporizing and separating chamber 55.

Cil

Although a high-pressure reaction chamber `is preferably employed in the relatively light oil cracking stage of the system it is within the scope of the invention, when desired, to introduce all or a regulated portion of the highly heated products from heating coil 44 directly into chamber 55 at any desired point or plurality of points in this zone, by well known means, not indicated in the drawing, the latter method of operation ordinarily being employed only when it is desired to produce relatively dry coke as the residual product in chamber 55.

Chamber 55 is preferably operated at a substantially reduced pressure relative to that employed in chamber 52 by means of which appreciable further vaporization of the liquid products supplied to this zone is accomplished. As previously mentioned, chamber 55 may be operated for the production of either liquid residue or coke. When liquid residue is produced in this zone it may be removed from the lower portion thereof through line 58 and valve 59 to cooling and storage or elsewhere, as desired. When coke is produced in chamber 55 it may be allowed to accumulate therein until the chamber is substantially i'llled or until its operation is completed for any other reason, following which it may be removed in any well known manner, not illustrated, and the chamber prepared for further operation. A

plurality of coking chambers may, of course, be

employed for this purpose, when desired, although only one is indicated in the drawing, and they may be operated simultaneously or alternately operated, cleaned and'prepared for further operation, Line 58 may serve as a drain-line when chamber 55 is operated for the production of coke and in addition may be utilized, when desired, as a means of introducing steam, water or any other suitable cooling material into the chamber after its operation has been completed in order to hasten cooling and facilitate removal of the coke. Line 58 may further serve, when desired, as a means of introducing hot oil, heated gases, steam or the like into chamber 55 to purge and precondition the same for operation.

Vaporous products are removed from the upper portion of chamber 55 and directed, in the case here illustrated, through line 60 and valve 6I to fractionation in fractionator Ill, wherein they commingle with the vaporous products from the relatively mild cracking stage of the system and are subjected therewith to fractionation for the formation of said relatively low-boiling and high- .boiling oils which Vare supplied, respectively, to heating coils 44 and l. It is, of course, also within the scope of the invention, although not illustrated, to employ separate fractionating means for the vaporous products of the relatively light oil cracking stage of the system, in which case the reflux condensate formed by said separate fractionation is separated into relatively lowboiling and high-boiling fractions which are returned, respectively, to heating coils 44 and 'I while the desired overhead product, preferably` comprising good quality motor fuel, may be separately recovered or may be recovered together with the nal light distillate product from fractionator I0. v

Fractionated vapors ofy the desired end-boiling point, preferably comprising materials within the boiling range of motor fuel and gas, are withdrawn from the upper portion of fractionator I0 and directed through line 28 and valve 29 to condensation and cooling in condenser 30. The resulting distillate and uncondensed gases pass through line 3I and valve 32 to collection and separation in receiver 33. The gases may be released from receiver 33 through line 34 and valve 35. Distillate may be withdrawn from receiver 33 through line 36 and valve 31 to storage or elsewhere, as desired. When desired, regulated quantities of the distillate collected in receiver 33 may be recirculated by well known means, not illustrated in the drawing, to the upper portion of fractionator I0 to serve as a refluxing and cooling medium in this zone for assisting fractionation of the vapors and to maintain the desired vapor outlet temperature therefrom.

Since careful control of the conversion time as well as the temperature and pressure conditions employed is an important feature of the invention, provision is made in the case here illustrated for cooling the cracked products to the desired degree at one or more points in the relatively heavy oil or mild cracking stage of the system. This is accomplished by diverting regulated quantities of the relatively low-boiling oil from line 4I through line 62 and valve 63 to cooler 64 wherefrom the cooled relatively low-boiling oil is discharged through line 65 and may be directed, A

quench the products passing to chamber I1.

Although any other suitable cooling material may be employed for this same purpose, such as, for example, a regulated portion or all of the charging stock or a regulated quantity of the relatively high-boiling oil removed from the lower portion of'fractionator I0, I preferably employ an oil which will be substantially completely revaporized by heat exchange with the materials which it serves to cool so that no appreciable amount of the cooling liquid will contaminate the residual product recovered from chamber I'I. However, in case the charging stock does not containl any appreciable quantity of high-boiling fractions undesirable as components of the residual product produced in chamber I1, the invention specifically contemplates the use of all or a portion of this charging stock as cooling material for the conversion products eventually supplied to chamber I1, whereby the non-vaporous high-boiling components of the charging stock may be recovered as a portion of the residual liquid from chamber I1 either Without being rst subjected to appreciable cracking or after being subjected to relatively mild cracking in chamber I4.

Cooling or quenching of the hot conversion products at one or more points in the relatively light oil cracking stage of the system is, of course, also within the scope of the invention although the numerous well known provisions for accomplishing this are not illustrated in the drawing.

The operating conditions which may be employed in an apparatus such as illustrated and above described to accomplish the desired result will, of course, vary With the type of charging stock employed and the type of products desired. The preferred range of such conditions is, however, approximately as follows: The heating coil of the relatively heavy oil or mild cracking stage of the system may employ an outlet conversion temperature ranging, for example, from 850 to 950 F., preferably with a superatmospheric pressure at this point in the system of from 100 to 500 pounds, or thereabouts, per square inch. When this stage of the system employs a high-pressure reaction chamber this zone may be operated at a superatmospheric pressure substantially the same or somewhat lower than that employed at the outlet from the heavy oil heating coil. The vaporizing chamber of a relatively mild cracking stage preferably employs a substantially reduced pressure relative to that maintained at the outlet from the heating coil of this stage and relative to that maintained in the preceding reaction chamber, when such a zone is utilized, this reduced pressure ranging, for example, from a superatmospheric pressure of 60 pounds, or thereabouts, per square inch, tosubstantially atmospheric pressure. The relatively light oil heating coil may employ an outlet conversion temperature ranging, for example, from 900 to 1050 F. and preferably employs an outlet pressure of from 200 to 800 pounds, or more, per square inch. The succeeding reaction chamber, when utilized, may be maintained at substantially the -same or a somewhat lower superatmospheric pressure. The vaporizing chamber of the relatively light oil cracking stage preferably employs a substantially reduced pressure relative to that in the reaction chamber or at the outlet from the preceding heating coil, in case no reaction chamber is utilized, ranging, for example, from a superatmospheric pressure of pounds, or thereabouts, per square inch down to substantially atmospheric pressure. The pressure employed in the fractionating, condensing and collectingv portions of the system may be substantially the same or somewhat lower than that employed in the preceding stage utilizing the lowest pressure.

As a specific example of the operation of the process accomplished Vin an apparatus such as illustrated and above described andutilizing, as charging stock, a mixture comprising equal parts `by volume of Oklahoma and North Texas topped Icrude having a gravity of 22 to 24 A. P. I. The 'charging stock is supplied tothe single fracrtionator of the system wherein it is separated,

together with the intermediate liquid conversion products, into fractions boilingabove and below approximately 630 F. The high-boiling oils removed from the lower portion of the fractionator are subjected in the relatively mild cracking coil to an outlet conversion temperature of approximately 925 F. with a superatmospheric pressure at theoutlet fromthe heating coil and in the .succeeding reaction chamber of approximately pounds per square inch. The stream of heated products entering the reaction chamber is cooled to a temperature of approximately 900 F.

by .the introduction thereto of a portion of the relatively low-boiling condensate recovered from the fractionator, the `cooling oilhaving a temperature of approximately 500 F. Liquid and vaporous conversion products `are removed in commingled state from the lower portion of the reaction chamber` without allowing any substantial volume of liquid to accumulate therein and the commingled materials are introduced into a vaporizing and separating chamber operated for the production of asphaltic residue and maintained at a superatmospheric ,pressure of `approximately 40 pounds: Vper square inch. The commingled vaporous and liquid conversion products passing from the reaction chamber to the vaporizing chamber are cooled to a temperature of approximately 785 F. partially by pressure reduction and partially by the introduction of another portion of the relatively light oil Stream from the fractionator. A motor fuel product of approximately 390 F. end-boiling point is recovered from the fractionator and the intermediate products boiling up to approximately 630o F., which are separately removed from the fractionator, are supplied to a separate heating coil wherein they are subjected to an outlet conversion temperature of approximately 960 F. and are thence passed through a succeeding reaction chamber maintained at a superatmospheric pressure of approximately 400 pounds per square inch wherefrom thev resulting vaporous and liquid conversion products are introduced into a separate vaporizing and separating chamber Penetration 93 50 gms. 5 sec.

77 F. `Melting point F 116 Duotility 100 Solubility CC14 99. 5 Solubility CS2 99. 7 Penetration 48 200 gms. 5 sec.

l Y 32 F.

I claim as my invention: 1. A process for the selective pyrolytic conversion of relatively low-boiling and relatively high-boiling hydrocarbon oils, which comprises subjecting an oil of relatively high-boiling characteristics to relatively mild conversion conditions of cracking temperature and.` superatmospheric pressure regulated to effect the production of a residual liquid product of the desired characteristics and lower boiling oils, cooling the resultant hot conversion products sufiiciently to prevent excessive continued conversion thereof, separating the total conversion products thus formed into vapors and said residual product in a zone of substantially reduced pressure relative to that at which they are produced, recovering said residual liquid from said reduced pressure Zone, subjecting the vaporous products to fractionation, whereby their components boiling above the range of the desired final light distillate product of the process are condensed as reux condensate and separated into selected relatively low-boiling and high-boiling fractions, returning said high-boiling fractions to said pyrolytic conversion, subjecting said selected lowboiling fractions ofthe reflux condensate to conversion in a separate cracking zone at higher temperature and under pressure conditions regulated to effect the production therefrom of high yields of good quality motor fuel, separating the resulting vapors and non-vaporous residue in a zone separate from that wherein the vaporous and residual liquid conversion products of the first mentioned cracking operation are separated, recovering said non-vaporous residue independently of said residual liquid from the reduced pressure Zone, subjecting the vaporous products from said separate Zone to said fractionation tions are separated, subjecting fractionated vapors of the desired end-boiling point to condensation, and recovering the resulting distillate.

2. A process as claimed in claim 1 wherein said cooling of the products of the rst mentioned cracking operation is accomplished, at least in part, by commingling therewith relatively lowboiling oil recovered from within the system which is not subjected thereby to appreciable cracking and which is substantially completely revaporized, whereby to avoid contamination with said liquid residue. Y

3. A process as claimed in claim 1 wherein charging stock for the process, comprising a hydrocarbon oil of relatively wide boiling range, is separated into selected lrelatively low-boiling and high-boiling fractionswhich are supplied, respectively, for cracking, to the light oil and heavy oil cracking stages.

4. A process as claimed in claim 1 wherein charging stock for the process, comprising a hydrocarbon oil of relatively wide boiling range, is supplied to said fractionating step.

5. A process as claimed in claim 1 wherein charging stock for the process, comprising a hydrocarbon oil of relatively high-boiling characteristics, is supplied to the first mentioned cracking stage.

6.Y A process as claimed in claim 1 wherein charging stock for the process, comprising a hydrocarbon oil which contains a substantial quantity of high-boiling fractionsY suitable as components of said residual liquid product, is supplied to the rst mentioned separating zone Wherefrom said residual liquid product is recovered.

'7. A process as claimed in claim 1 wherein a portion of the total charging stock for the process, comprising hydrocarbon oil of relatively highboiling characteristics, is subjected to conversion in the first cracking stage of the system and another portion of the total charging stock, comprising hydrocarbon oil of relatively low-boiling characteristics, is subjected to conversion in the second mentioned cracking stage.

8. A process for the selective pyrolytic conversion of relatively low-boiling and high-boiling hydrocarbon oils, which comprises subjecting an oil of relatively high-boiling characteristics, which may be converted under controlled conditions of relatively mild cracking temperature, substantial superatmospheric pressure and relatively short time to produce substantial yields of marketable asphaltic residue and lower boiling oils, to such conversion conditions, separating the desired resultant asphaltic products, in the form of non-vaporous residue, from the lower boiling products in vaporous state, recovering the former, subjecting said vaporous products to fractionation to recover therefrom desirable low-boiling components, such as motor fuel, separating their remaining components into selected relatively low-boiling fractions which will yield neither substantial quantities of additional motor fuel nor an asphaltic residue of the desired characteristics under the conversion conditions to which said relatively high-boiling oil is subjected, and higher boiling fractions which will be appreciably cracked under said conversion conditions to yield additional quantities of desirable asphaltic residue and lower boiling products, returning said high-boiling fractions to said conversion step, subjecting said low-boiling fractions in a separate cracking step to conversion conditions of relatively higher `temperature regulated to eiect the production of high yields of good quality motor fuel, a substantially non-asphaltic residue and intermediate products, separating the resultant vapors and substantially non-asphaltic residue in a zone separate from that wherefrom said asphaltic residue is recovered and recovering the non-asphalt residue independently of the asphaltic residue, and subjecting the vaporous products from the last mentioned cracking operation to said fractionation wherein said low-boiling and high-boiling fractions Vare separated.

9. A process for the selective pyrolytic conversion of relatively low-boiling and high-boiling hydrocarbon oils, which comprises subjecting an oil of relatively high-boiling characteristics, which may be converted under controlled conditions of relatively mild cracking temperature, substantial superatmospheric pressure and relatively short time to produce substantial yields of marketable asphaltic residue and lower boiling oils, to such conversion conditions, separating the desired resultant asphaltic products, in the form of nonvaporous residue, from the lower boiling products in vaporous state, recovering the former, simultaneously subjecting a relatively low-boiling hydrocarbon oil, which will yield neither substantial quantities of motor fuel nor a marketable asphaltic residue under the cracking conditions to which said relatively high-boiling oil is subjected, to conversion conditions of relatively higher cracking temperature under substantial superatmospheric pressure in a separate cracking zone, separating the vaporous and non-vaporous residual products of the last mentioned cracking operation out of contact with said asphaltic residue produced in the rst mentioned cracking operation, recovering the residual product of the last mentioned cracking operation, independently of said asphaltic product, subjecting the vaporous products of both cracking operations to fractionation in commingled state for the recovery therefrom of desirable low-boiling components, such as motor fuel, and separation of their remaining components into relatively low-boiling and high-boiling fractions, returning said lowboiling fractions to said separate cracking step, and returning the high-boiling fractions which do not contain any substantial quantity of materials boiling below 600 F. to the iirst cracking step.

10. A process for the selective pyrolytic conversion of relatively low-boiling and high-boiling hydrocarbon oils, which comprises subjecting an oil of relatively high-boiling characteristics, which may be converted under controlled conditions of relatively mild cracking temperature, substantial superatmospheric pressure and relatively short time to produce substantial yields of marketable asphaltic residue and lower boiling oils, to such conversion conditions, separating the desired resultant asphaltic products, in the form of nonvaporous residue, from the lower boiling products in vaporous state, recovering the former, simultaneously subjecting a relatively low-boiling hydrocarbon oil, which will yield neither substantial quantities of motor fuel nor a marketable asphaltic residue under the cracking conditions to which said relatively high-boiling oil is subjected, to conversion conditions of relatively higher cracking temperature under substantial superatmospheric pressure in a separate cracking zone, separating the vaporous and non-vaporous residual products of the last mentioned cracking operation out of contact with said asphaltic residue produced in the first mentioned cracking operation,

recovering the residual product of the last mentioned cracking operation independently of said asphaltic product, subjecting the vaporous products of both cracking operations to fractionation in commingled state with hydrocarbon oil charging stock for the process, whereby to recover from the commingled materials desirable low-boiling components, such as motor fuel, and separate their remaining components into relatively lowboiling and high-boiling fractions, returning said 10W-boiling fractions to said separate cracking step, and returning the high-boiling fractions which do not contain any substantial quantity of materials boiling below 606 F. to the rst cracking step.

11. A process for the selective pyrolytic conversion of relatively 10W-boiling and high-boiling hydrocarbon oils, Which comprises subjecting an oil of relatively high-boiling characteristics to relatively mild conversion conditions of cracking temperature and superatmospheric pressure in a heating coil and communicating enlarged reaction chamber, separating the resulting vaporous and liquid conversion products, subjecting the latter to appreciable further vaporization in a reduced pressure vaporizing and separating chamber, recovering the resulting non-Vaporous liquid residue, simultaneously subjecting an oil of relatively loW-boiling characteristics to conversion conditions of relatively higher cracking temperature under superatmospheric pressure in a separate heating coil, introducing the heated products from said separate heating coil into a separate enlarged reaction chamber, removing vaporous and liquid conversion products from said separate reaction chamber, subjecting the latter to appreciable vaporization in a separate reduced pressure Vaporizing and separating chamber, and recovering the resultant residue independently of the first-named residue, commingling the vaporous conversion products from both cracking operations and subjecting the commingled vapors to fractionation, together with hydrocarbon oil charging stock for the process, whereby the components of the commingled materials boiling above the range of the desired final light distillate product of the process are condensed as reflux condensate and separated into selected relatively lowboiling and high-boiling fractions, supplying the high-boiling fractions for cracking to the rst mentioned heating coil, supplying the 10W-boiling fractions to cracking to said separate heating coil, subjecting fractionated vapors of the desired endboiling point to condensation, and recovering the resulting distillate.

EDWIN F. NELSON. 

